1. Field of the Invention
This invention relates data processing for geophysical exploration and oil production, more specifically related to attenuate noises in marine seismic data, to attenuate seismic interference noises.
2. Description of the Related Art
Seismic exploration is the most widely used geophysical exploration. It involves surveying subterranean geological formations for hydrocarbon deposits. A survey typically involves deploying seismic source(s) and seismic sensors at predetermined locations. The sources generate seismic waves, which propagate into the geological formations creating pressure changes and vibrations along their way. Changes in elastic properties of the geological formation scatter the seismic waves, changing their direction of propagation and other properties. Part of the energy emitted by the sources reaches the seismic sensors. Some seismic sensors are sensitive to pressure changes (hydrophones), others to particle motion (e.g., geophones), and industrial surveys may deploy only one type of sensors or both. In response to the detected seismic events, the sensors generate electrical signals to produce seismic data. Analysis of the seismic data can then indicate the presence or absence of probable locations of hydrocarbon deposit.
Depending on the area being surveyed, there are marine seismic survey, which is done in open water, or land seismic survey which is done on land; or transition zone, which is done on shallow water or marsh land. For “marine” surveys, which are conducted in open water, they can be conducted not only in saltwater environments, but also in fresh and brackish waters. In one type of marine survey, called a “towed-array” survey, an array of seismic sensor-containing streamers and sources is towed behind a survey vessel
In seismic exploration, removing noises from various sources while preserving desired signal is always a challenge.
In the marine environment, the signals from other seismic vessels in adjacent areas are one type of major noises. Strong seismic interference (SI) noises generated by other seismic acquisition vessels are common in petroleum exploration basins. When the SI is particularly strong, the processed data may still contain high level of SI noises and may make the data unusable.
Conventionally, SI noise attenuation can be performed either in Offset-Time (X-T) Common Midpoint Gather (CMP) domain or Time-slowness (Tau-P) domain using amplitude discrimination of SI noise from surrounding signal in a 2D approach. Frequency-Wavenumber (FK) domain may also be used where FK filtering is done by others to help in attenuating the SI noise. Noise predictions in f-x or f-x-y domains were also suggested to attenuate SI noises. Other generic noise attenuation methods have been used to treat SI noises.
These conventional methods attenuate some SI noise to some extent, but fail to attenuate the SI trend. The conventional methods tend to remove some of the SI noise but leave a discontinuous trend of residual SI noise.
Several conventional methods are described by the following papers, or patent publications, which are incorporated by references:
Akbulut, K., Saeland, O., Farmer, P. and Curtis, J., Suppression of seismic interference noise on Gulf of Mexico data. In 54th Annual International Meeting of Society of Exploration Geophysicists, Expanded Abstracts, 1984, pp. 527-529
Mitchell, A. et al, Efficient tau-p hyperbolic velocity filtering, Geophysics, Vol 55, No. 5, (May 1990), p 619-625
Noponent, I. et al, Attenuation of waterborne coherent noise by application of hyperbolic velocity filtering during tau-p transformation, Geophysics, Vol 51, No. 1, (January 1986), p 20-33
Schultz, P., Seismic data processing: current industry practice and new directions, Geophysics, Vol 50, No. 12, (December 1985), p 2452-2457
Lynn, W., Doyle, M., Lamer, K. and Marschall, R., Experimental investigation of interference from other seismic crews. Geophysics, 1987, 52, 1501-1524
Karsli, H. et al., Application of complex-trace analysis, Geophysics, Vol 71, No. 3, (May 2006), p V79-V86
Gulunay, N. et al, Spatial prediction filters for attenuation of seismic interference noise, SEG Expanded Abstracts, CR1837
Gulunay, N., Two different algorithms for seismic interference noise attenuation. Leading Edge, February 2008, p 176-181
Gulunay, N., Magesan, M. and Baldock, S., Seismic interference noise attenuation. In 74th Ann. Internat., Mtg., SEG, Expanded Abstracts, 2004, pp. 1973-1976
Huaien, W., Guangxin, L., Curtis, E. H. and Snyder, F. C., Attenuation of marine coherent noise. In 59th Annual International Meeting of Society of Exploration Geophysicists, Expanded Abstracts, 1989, pp. 1112-1114
Lie, J. E., Seismic Interference, Filtering Methods and Revised Noise Limits; A/S Geoteam; Oceanology '88: Proceedings of an international conference, Mar. 8-11, 1988, Brighton, UK
Rajput, S. et al., Attenuating the seismic interference noise on three-dimensional seismic data by frequency—receiver—shot (f-x-y) prediction filters; Schlumberger Reservoir Seismic Services, Mumbai, India National Geophysical Research Institute, Hyderabad 500 007, India, Department of Geophysics, Indian Institute of Technology, Roorkee 247 667, India
The US patent publications include: U.S. Pat. Nos. 6,446,008, 4,760,563, 6,651,007, 5,448,531, 7,366,054, 7,591,491, 7,564,740, 7,239,578, 6,691,039, 4,937,794, 5,971,095, 5,014,249 and 5,818,795.
It is desirable to have a method to attenuate SI noises more efficiently and without leaving too much residual noises.